Pressure responsive magnetic switch

ABSTRACT

A housing supports a magnetically operated contact unit and a permanent magnet switch operator, such as a tubular cylinder containing a fluid pressure responsive magnetic piston.

United States Patent 1191 Ochsner 1 1 Dec. 2, 1975 [5 PRESSURE RESPONSIVE MAGNETIC 3.342959 9/1967 Breunich 335/205 SWITCH 3,366,758 1/1968 Bentzen at a] 335/ S 3,429,291 2/[969 Hoffman ZOO/81.9 M Inventor: Rolf H- OchSner, Milford, C n- 3,450,853 6/1969 Snyder 335/205 3,507,359 4/1970 Wurnock... ZOO/81.9 M [73] Asbgnee' Rfbertshaw Comm 3,549,837 12/1970 Barnes ZOO/81.9 M

Richmond, Va.

[22] Filed: Mar. 27, 1974 i Primary E.raminerGerald P. Tolin [21] Appl 455451 Attorney, Agent, or FirmAnthony A. OBrieu [52] US. Cl. 200/82 R; 200/81.9 M; 340/244 E; 335/205 511 int. c1. HOIH 35/38 ABSTRACT {58] Field of Search 335/205-207; 1

210/; 73/205 R, 308; 116/70; 340/52 C, A housing supports a magnetically operated contact 244 E; 200/81 R, 81.9 M, 82 R, 82 A, 82 D, unit and a permanent magnet switch operator, such as 83 L, 84 C a tubular cylinder containing a fluid pressure responsive magnetic piston. [56] References Cited UNITED STATES PATENTS 12 Claims, 8 Drawing Figures 3,285,183 ll/l966 Hembree et a1 200/83 L 30 I80 I84 54 48 88 8 24 8 p 186 I88 4 e0 52 3 9| i A 38 -l64 34 I62 224 228 22 1143 230 138 137 1 0 1 Z 4 l 232 146 148 I44 US. Patent Dec. 2, 1975 Sheet 1 of? 3,924,086

U.S. Patent Dec. 2, 1975 Sheet 2 of3 3,924,086

US. Patent Dec. 2, 1975 Sheet 3 of3 3,924,086

FIG 7 FIG 8 FIG 6 PRESSURE RESPONSIVE MAGNETIC SWITCH BACKGROUND OF THE INVENTION 3,549,837, contains a number of magnetic switch devices including pressure responsive switches utilizing slidable permanent magnet pistons for operating sealed switch contact units. some of the prior art pressure responsive switches employ an arrangement of parts which are relatively expensive to manufacture, difficult to assemble, or unreliable. Another deficiency of some prior art switches employing sealed contact units is-that the movement of the permanent magnet, and hence the pressure, required to operate the contact unit is subject to a wide variation. Further, other pressure responsive switches employ an excessive number of sealed components, such as threaded fittings, increasing the tendency of the switches to leak at the fluid pressures employed. Still further, the prior art magnet switch devices often were prone to fail or operate unreliably when subjected to vibration.

SUMMARY OF-THE INVENTION rigid leads having an end portion bent substantially perpendicular to the second axis, and the housing having an opening for receiving and holding the bent end portion such that the sealed contact unit is held in a predeterminedrotative orientation about the second axis.

An object of the invention is to construct a magnetic switch employing relatively inexpensive parts which can be easily assembled to produce a highly reliable switch.

Another object of the invention is to eliminate stress onleads extending from sealed contact units.-

It is also an object of the invention to reducethe susceptibility of pressure responsive switches to leakage.

A further object of the invention is a pressure switch construction which withstands a relatively high level of vibration without failure or faulty operation.

Additional features of the invention include the provision of a housing structure having a cavity with first supporting projections for supporting a switch contact unit and second supporting projections forsupporting a cylinder and magnetic piston assembly; and the provision of a box-like housing structure having a wall through which terminals extend from a cavity wherein projections support a permanent magnet switchoperator next to a switch contact unit which is electrically connected to the terminals. j I

taken along 1ines'6'6 of FIG. 4.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation cross section of a magnetic switch device constructed in accordance with the invention. 1

FIG. 2 is a top view ofthe switch device of FIG. 1.

FIG. 3 is a side cross section view of the switch device taken along line 33 of- FIG. 1;

FIG.-4 is an elevation cross section view of a housing of the switch device of FIG. 1.

.FIG. '5 is a top view of the housing of FIG. 4.

FIG. 6 is aside cross section view of the housing FIG. 7 is a detailed view of a sealed switch contact unit of the switch device of FIG. 1.

FIG. 8 is'a detailed cross section view of a permanent magnetic piston assembly unit for the switch device of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in FIG. 1, the invention is embodied in a magnetic switch device including a housing, indicated generally at 20, supporting a sealed contact unit, indicated generally at 22, and a cylinder and magnetic piston assembly, indicated generally at 24. The sealed contact unit 22 and the assembly 24 are held adjacent or in close proximity along side each other so that the cylinder andmagnetic piston assembly 24 can readily and reliably operate the sealed contact unit 22.

The cylinder and magnetic piston assembly 24 has a tubular cylinder or member 30 with an end wall 32, the

tubular member 30 and wall 32 integrally formed from a non-magnetic material, such as a phosphor bronze alloy. The other end of the tubular member 30 has an enlarged portion 34 containing a plug member 36 formed from a suitable material such as brass. The plug member 36 is retained within the open end of the tubular member 30 by an inwardly formed lip 38 of the tubular member 30 securing the outer peripheryof the plug member 36 against a shoulder 40 formed between the enlarged portion 34 and the non-enlarged portion of the tubular member 30. An input conduit or tube 42 is secured within an opening 44 at the right end of the tubular member 30 as viewed in FIG. 1. Similarly a exhaust or low pressure conduit or tube 46 is secured within a opening 48 at the left end in the enlarged portion 34 of the tubular member 30. Both tubes 42 and 46 extend radially from an axis 49 of the tubular member 30. The tube 46 opens into a recess 50in the plug member 36communicating between the tube 46 and the interior of the tubular member 30. Conveniently the plug member 36 and the tubes 42, 46 and the plug 36 are sealed to the tubular member 30 by respective welds 52, 54 and 56.

As shown in FIG. 8 a magnetic piston for the cylinder and piston assembly 24 of FIG. 1 has a cylindrical permanent magnet 58, such as an ALNICO V permanent magnet, supported by guide members 60 and 62. The guide members 60 and 62 are made of a suitably nonmagnetic material, such as nylon, and have respective cylindrical cavities 64 and 66 coaxial with the axis 49 for receiving respective ends of the cylindrical magnet 58. Circumferentially disposed resilient bosses 68 and 70 extending within the respective cavities 64 and 66 from the guide members 60 and 62 engage the outer surface of the cylindrical magnet 58 to frictionally secure the guide members to the magnet 58. The outer 3 peripheries of the guide members 60 and 62 are generally cylindrical to mate with the internal surface of the tubular member 30 and to slide the magnet 58 along the axis 49. The guide member 62 has a cylindrical extension 72 upon which a cup washer 74, made of a resilient material such as polytetrafluoroethylene, is held by a rigid non-magnetic backup washer 76, such as a brass washer, secured by a staked shoulder portion 78 of the cylindrical extension 72. Also the guide member 62 has a cylindrical spacing projection of 80 which extends along the axis 49. Similarly a protruding end 82 of the guide member 60 extends coaxial the axis 49 and has a reduced diameter thus fonning an annular shoulder 84 on the outer periphery of the guide member 60.

Referring back to FIG. 1, a compression spring 86 is positioned at one end over the projecting end 82 against the shoulder 84 of the guide member 60 while at its other end engages a annular surface 88 of a spring retainer 90. The spring retainer 90 has a inwardly deformed cup-like portion 91 which is engaged by an end of a adjustment screw 92 suitably threaded within a threaded bore 94 extending along the axis 49 through the plug member 36. The spring 86 normally urges the projecting end 80 against the end wall 32 to determine the unoperated position of the magnetic piston within the tubular cylinder 30. The left most position of the magnetic piston is determined by the projecting portion 82 engaging the portion 91 of the retainer 90 or by the fully compressed position of the spring 86.

As illustrated in FIG. 7 the sealed contact unit 22 has a tubular non-magnetic sealed enclosure, such as a glass enclosure 96, enclosing reed or blade contacts 98 and 100 extending substantially parallel an axis 102 with overlapping-but-spaced end contact portions. The outer ends of the reed contacts 98 and 100 are attached to integrally formed leads 104 and 106 which extend through end sealed portions 108 and 110 of the enclosure 96 and protrude beyond the enclosure 96. The reed contacts 98 and 100 are formed into resilient flat reeds or strips from a ferromagnetic material of low magnetic retentivity. End portions 112 and 114 of the respective leads 104 and 106 are bent at a 90 degree angle to the axis 102 to extend in substantially the same direction from the axis 102. Also the bent portions 112 and 114 extend substantially perpendicular to the largest flat surfaces of the reeds 98 and 100.

As shown in FIGS. 4, and 6, the housing has an upper portion with a generally elongated box-like configuration having opposite side wall portions 116 and 118, opposite end wall portions 120 and 122, and a bottom portion 124 forming a cavity 126. The housing 20 may be made, for example molded, from any suitable non-magnetic rigid material, such as LEXAN 141, a polycarbonate sold by General Electric Co., Inc. A pair of projections, ribs or projecting walls 128 and 130 extend into the cavity 126 and transversely across the bottom portion 124 of the housing 20 and have notches or grooves 132 and 134 formed in the upper edges of the ribs 128 and 130 parallel to the axis 49 for retaining the enclosure 96 of the sealed contact unit 22. A recess 136 formed between the ribs 128 and 130 contains a resilient potting compound 137, FIG. 1, such as a silicone rubber compound like RTV-102 or RTV-l08 sold by General Electric Co., Inc., to resiliently support the sealed contact unit 22. Spaced on opposite sides of the partitions 128 and 130 are parallel openings or bores 138 and 140 for receiving the respective deformed portions 112 and 114 of the sealed contact unit. The bore 138 has a beveled entrance tapering down to a lower cylindrical portion which has a tolerance or diameter designed to closely hold the deformed portion 112. The opening has a similarly beveled entrance tapering down to a lower cylindrical portion which has a substantially larger tolerance or diameter to allow for some manufacturing variance between the bent portions 1 12 and 114 to prevent stressing of the sealed portions 108 and 110 of the contact unit 22.

As illustrated in FIGS. 1 and 3 flat quick disconnect electrical terminals 142 and 144 are secured into respective slots 146 and 148 through the bottom portion of the housing. Each of the terminals 142 and 144 has an upper enlarged portion 150 which forms shoulders 152 engaging shoulders 154 in the slots 146 and 148. The terminals 142 and 144 are secured below the slots 146 and 148 on the bottom portion of the housing 20 by staked or deformed portions 156 of the terminals. The upper end of the terminals 142 and 144 have notches 158 formed therein for receiving the leads 104 and 106. Flexible electrical conductors 160 and 162 are welded at one end to the respective bent lead portions 112 and 114 and at other ends to respective terminals 142 and 144 to form an electrical connection between the terminals 142 and 144 and the respective leads 104 and 106. The flexible strip conductors 160 and 162 are a suitable material, such as NICI-IROME V alloy ribbon wire, selected for their flexibility to avoid placing any residual stress on the leads 104 and 106 and for their suitability for welding to the leads 104 and 106 and terminals 142 and 144. A flexible sheet 164 is positioned between the contact unit 22 and the cylinder and piston assembly 24. The sheet 164 is made from a suitable non-magnetic, electrically insulating and vibration absorbing material, such as vulcanized fiber often called fish paper.

As shown in FIGS. 4, Sand 6 the housing 20 has a supporting projection 166 extending from the corner of the end wall portion 122 and bottom wall portion 124 for supporting the end 32 of the tubular cylinder 30. At the opposite end wall portion 120, a supporting projection 168 extends upward from the bottom wall portion 124 supporting the end portion 34 of the tubular cylinder 30. Projections 170 and 172 from the side wall portion 116 and projections 174 and 176 from the side wall portion 118 extend inwardly into the cavity 126 to retain the cylinder and magnetic piston assembly 24 centrally within the cavity 126. The end wall 120 has a opening 178 formed therein for receiving a protruding end of the plug 36 and for exposing the bore 94 so that the adjustment screw 92 can be easily adjusted after assembly.

As shown in FIGS. 1, 2 and 3, a bow spring 180 is urged against the upper portion of the cylinder and piston assembly 24 by a cover 182. The cover 182 has downward projecting end tabs 184 and 186 extending into mating grooves 188 and 190 formed within the end wall portions 120 and 122. The cover 182 has bent side wings 192 and 194 with respectively inwardly turned lips 196 and 198 for securing the cover to an outward extending flanges 200 and 202 from the side wall portions 116 and 118 of the housing 20. The cover 182 has notches 204 and 206 which together with respective notches 208 and 210, FIG. 4, in the upper edge of the wall 118 form a opening through which the respective tubes 46 and 42 extend. Notches or openings 212 and 214 formed on the opposite side of the cover 182 are provided for allowing a potting material 216 to be inserted for securing the tubular cylinder 30 to housing 20. The potting material may be a relatively rigid material, such as a polymer formed from an epoxy resin mixture of an epoxide, EPOSET M-5, and a curing agent, EPOCURE-78, purchased from Hardman, Inc, of Belleville, New Jersey.

The lower portion of the housing has walls 220 and 222 which surround the outside extending portions of the respective terminals 142 and 144 to protect the terminals from being bent or damaged during storage and handling. Also the housing 20 has an outwardly extending flange 224 with holes 228 and 230 formed therein for receiving a securing screw or bolt. Conveniently a gasket 232 may be attached to the bottom of the flange 224 for sealing the pressure responsive switch device to a suitable cabinet or the like on a motor housing.

In the assembly of the magnetic switch device of FIGS. 1, 2 and 3, the terminals 142 and 144 are inserted within the slots 146 and 148 and the shoulder portions 156 and staked to firmly secure the terminals to the housing 20. The flexible conductors 160 and 162 are bonded at one end to the respective conductive bent end portions 1 12 and 1 14 of the leads 102 and 104 of the contact unit 22.

A predetermined quantity of flexible potting compound 137, in a viscous state, is poured into the recess 136. The switch unit 22 is then pressed into the potting compound to the position shown inserting the bent lead portions 112 and 114 into the respective openings 138 and 140 in the bottom portion of the housing. Then the free ends of the flexible conductive strips 160 and 162 are welded to the tops of the respective terminals 142 and 144.

The tubes 42 and 46 are welded in the respective openings 44 and 48 of the tubular cylinder 30. The cup washer 74 and the backup washer 76 are assembled and secured on the cylindrical extension 72 by staking the shoulder 72 of the guide member 62. The guide member 62 and the guide member 60 are pressed over the opposite ends of the cylindrical magnet 58 to form the magnetic piston assembly which is then inserted within the open end of the tubular cylinder 30 with the projection 80 engaging the end wall 32. The spring 86 is inserted against the annular shoulder 84 and the spring retainer 90 is inserted ontop of the spring 86. Then the plug 36 is installed in the enlarged portion 56 of the tubular cylinder 30 and the lip 38 is deformed inwardly to secure the plug 36 in the cylinder 30. Thereafter the lip 38 may be welded to the plug 36 to insure 6 upper portion of the cavity 182 through the openings 212 and 214.

Subsequently the tube 42 is connected to a standard fluid pressure supply while the tube 46 is connected to a low pressure side of the standard pressure supply. The screw 92 is adjusted to produce a desired operation of the switching unit 22 as monitored through the terminals 142 and 144. The outward extending end of the adjustment screw 92 may then be sealed to the plug member 36 by solder or other sealing material.

In operation of the fluid pressure switch, pressure applied through the inlet tube 42 exerts a pressure against the cup washer 74 causing the magnetic piston including the guide members 60 and 62 and the permanent magnet 58 to move to the left within the tubular cylinder against the force of the spring 86. When the pressure is sufficient, the magnet 58 will be sufficiently moved to the left over the switching unit 22 where the sufficient magnetic flux from the permanent magnet 58 will pass through the magnetic reeds 98 and 100 in the switching unit 22 causing the resilient reeds 98 and 100 to close completing an electrical circuit between terminals 142 and 144. If the pressure on the inlet tube 42 should drop the piston assembly will retract under the force of the spring 86 removing the magnetic flux from the reeds contacts 98 and 100 allowing the resilient nature of the reed contacts 98 and 100 to electrically open the switch unit 22.

that the cylinder is tightly closed. Subsequently the adjusting screw 92 is screwed into the threaded bore 92 to complete the cylinder and piston assembly 24.

The sheet 164 is placed over the assembled contact unit 22 assembled in the lower portion of the cavity 126 and the cylinder and magnetic piston assembly 24 is then positioned in the upper portion of the cavity 126 above the supporting projections 166 and 168. The cylinder and magnetic piston assembly is retained centrally within the cavity 126 by projections 170, 172, 174 and 176. Then the bow spring 180 is placed on top of the cylinder and magnetic piston assembly 24 and the cover 182 is assembled with the tabs 184 and 186 fitting into the respective slots 188 and 190. The wings 192 and 194 are bent inwardly to engage the lips 196 and 198 with the underneath portions of the flanges 200 and 202 to secure the cover 182 to the housing 20. Then the potting compound 216 is poured into the Improved reliability and uniformity in operation of different magnetic switch devices are made possible by the bent lead portion 112 received and retained by the opening 138. The operation of the reed contacts 98 and is dependent upon their rotative position about the axis 102 relative to the axis 49 of the magnetic 58. Having the bent lead portion 112 extending in the same predetermined direction relative to facing flat surfaces of the reeds 98 and 100, such as perpendicular, results in the assembly of different switch devices having their reed contacts 98 and 100 in the same rotative position relative to the magnet 58.

Additionally the particular construction of the tubular cylinder 30 with the integrally formed end wall 32 and the plug member 36 secured within the enlarged cylindrical portion 34 by the inwardly extending lip results in an improved cylinder for a fluid pressure operated magnetic piston which is less prone to leak.

The switch device is particularly suitable for use in sensing the pressure of a lubricating fluid in a machine, such as an electric motor and compressor in refrigeration or cooling systems, by connecting the tube 42 to the high pressure side of an oil pump and connecting the tube 46 to the low pressure side of the oil pump. The magnetic switch device is capable of withstanding a high degree of vibration without failure. Having the bent lead portion 114 assembled in the bore with a large tolerance as well as the use of the flexible conductors and 162 for connecting to the leads 102 and 104 prevents stress on the seal portions 108 and 110 of the switch unit; such stress, particularly where subject to vibration, can result in breakage and failure of the enclosure 96 and the contact unit 22. Additionally the vibration resistance of the enclosure 96 is improved by the use of the resilient potting compound 137 and the vibration energy absorbing sheet 164. The resilient nature of the potting compound 137 also tends to produce uniform operation in different switch devices due to its bias of the switch unit 22 toward the cylinder and magnetic piston assembly 24.

Since many modifications, variations and changes in detail can be made to the particularly described embodiment, it is intended that all matters in the foregoing description and accompanying drawing be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A pressure responsive magnetic switch comprising a non-magnetic housing having a plurality of wall portions forming a cavity;

a magnetically operated switch contact unit;

a plurality of first projections extending into the cavity from the wall portions and supporting the switch contact unit in a first location in the cavity;

a switch operator including a tubular non-magnetic cylinder, a permanent-magnetic piston slidable in the cylinder, and first and second conduits communicating with respective ends of the tubular cylinder;

a plurality of second projections extending into the cavity and retaining the tubular cylinder in a second location in the cavity adjacent the switch contact unit;

terminal means mounted in the housing and extending outside the housing from the cavity; and

means in the cavity electrically connecting the switch contact unit to the terminal means.

2. A pressure responsive magnetic switch as claimed in claim 1 wherein the magneticallyoperated switch contact unit includes a tubular non-magnetic sealed enclosure, a pair of magnetic reed contacts, and a pair of leads attached to the respective reed contacts and extending through seals of the enclosure; and

each of the plurality of first projections has a groove for retaining the sealed enclosure.

3. A pressure responsive magnetic switch as claimed in claim 2 wherein the non-magnetic housing is elongated and has a pair .of opposite side wall portions, 21 pair of opposite end wall portions and a bottom wall portion forming the cavity,

the plurality of first projections includes a pair of parallel ribs transverse to the side wall portions and extending upward from the bottom wall portion,

said groove is formed in the top of the parallel ribs,

and

the plurality of second projections includes a pair of projections adjacent the respective opposite end wall portions extending upward from the bottom wall portion to a height above the parallel ribs.

4. A pressure responsive magnetic switch comprising a pair of magnetic switch contacts,

a non-magnetic tubular cylinder having an integrally formed wall closing one end,

means mounting the pair of magnetic switch contacts adjacent the tubular cylinder,

a plug secured in and sealing the other end of the tubular cylinder,

a first tube communicating into the tubular cylinder adjacent the one end,

a second tube communicating into the tubular cylinder adjacent the other end, and

a piston including a permanent magnet slidably supported in the tubular cylinder.

5. A pressure responsive magnetic switch as claimed in claim 4 wherein the tubular cylinder has an enlarged tubular portion at the other end forming a shoulder at the edge of 8 the enlarged tubular portion, and an inwardly deformed lip securing the plug in the other end against the shoulder.

6. A pressure responsive magnetic switch comprising a pair of magnetic switch contacts,

a non-magnetic tubular cylinder having an integrally formed wall closing one end,

means mounting the pair of magnetic switch contacts adjacent the tubular cylinder,

a plug secured in the other end of the tubular cylinder,

said plug having a threaded bore coaxial with an axis of the tubular cylinder,

a first tube communicating into the tubular cylinder adjacent the one end,

a second tube communicating into the tubular cylinder adjacent the other end,

a piston including a permanent magnet slidably supported in the tubular cylinder,

an adjustment screw in the threaded bore having an end extending into the tubular cylinder,

a spring retainer movably engaged by the end of the adjustment screw in the tubular cylinder, and

a compression spring between the spring retainer and the piston.

7. A pressure responsive magnetic switch comprising a magnetically operated switch contact unit,

a non-magnetic tubular cylinder,

means mounting the switch contact unit along side of the tubular cylinder,

a first conduit communicating into one end of the tubular cylinder,

a second conduit communicating into the other end of the tubular cylinder,

a cylindrical permanent magnet in the tubular cylinder,

a pair of guides having a pair of facing cylindrical cavities receiving respective ends of the cylindrical permanent magnet and slidably supporting the cylindrical magnet in the tubular cylinder,

a resilient cup washer,

a rigid backup washer, and

means securing the backup washer and the cup washer to one of the pair of guides to form a piston seal in the tubular cylinder.

8. A pressure responsive magnetic switch as claimed in claim 7 wherein the securing means includes a cylindrical extension on one of the guides extending coaxial with the tubular cylinder and upon which the cup washer and backup washer are mounted,

a staked end portion of the cylindrical extension securing the backup washer and the cup washer to the one guide.

9. A pressure responsive magnet switch comprising a sealed contact unit including a sealed tubular enclosure of glass, a pair of resilient magnetic reed contacts extending into an overlapping relationship within the enclosure, and a pair of leads attached to the reed contacts extending through seals at the respective ends of the enclosure;

a housing made from a rigid non-magnetic material;

means including a resilient material mounting the contact unit on the housing; I

a switch operator including a rigid non-magnetic tubular cylinder, a piston having a permanent magnet slidable in the tubular cylinder, and tubular means communicating-with respective ends of the tubular cylinder;-'- I means mounting the switch operator on the housing such that the resilient material urges the sealed tubular enclosure toward the switch operator;

a vibration energy absorbing non-magnetic material between the contact unit and the switch operator; and

said means mounting the switch operator holding the switch operator against one side of the vibration energy adsorbing material.

10. A pressure responsive magnetic switch as claimed in claim 9 wherein the energy absorbing material is a :sheet of vulcanized fiber.

1 l. A pressure responsive magnetic switch as claimed in claim 9 wherein the resilient material is a resilient potting compound,

and

the means mounting the switch operator includes a rigid potting compound.

12. A fluid pressure responsive switch device comprising an elongated sealed magnetic contact unit having a non-magnetic tubular glass enclosure with a pair of resilient magnetic reed contacts extending in opposite directions from overlapped contact portions substantially parallel to an axis of the tubular enclosure;

a pair of rigid leads attached to the respective pair of resilient reed contacts and extending in opposite directions along the enclosure axis through respective seals at the ends of the tubular enclosure;

said pair of leads having end portions bent perpendicular to the enclosure axis to extend in the same di? rection from the enclosure axis;

a non-magnetic tubular cylinder having a cylinder axis and an integrally formed closed end wall and having an enlarged cylinder portion adjacent to the other end forming an annular shoulder;

an inlet tube communicating radially into the tubular cylinder adjacent the closed end wall;

an exhaust tube communicating radially into the en- I larged cylinder portion of the tubular cylinder;

a cylindrical permanent magnet;

a pair of non-magnetic guides having cylindrical cavities coaxial with the cylinder axis;

said guides having bosses projecting radially inward the cavities frictionally retaining respective ends of the cylindrical permanent magnet;

a cylindrical extension on one of said pair of guides coaxial with the cylinder axis;

a resilient cup washer on the cylindrical extension;

a backup washer on the cylindrical extension;

a staked shoulder portion of the cylindrical extension securing the backup washer and resilient cup washer to the one guide;

a spacing projection extending from the one guide coaxially with the cylinder axis;

said pair of guides, permanent magnet, cup washer, and backup washer forming a magnetic slidable piston in the tubular cylinder;

a plug in the enlarged cylindrical portion;

an annular lip on the end of the enlarged cylindrical portion securing the plug between the annular lip and the annular shoulder;

said plug having a channel formed in the periphery thereof allowing communication from the interior of the tubular cylinder to the exhaust tube;

a threaded bore extending through the plug coaxial with the cylinder axis;

an adjustment screw extending from the threaded bore into the interior of the tubular cylinder;

a spring retainer in the tubular cylinder and having an annular flange and a cup shaped center engaged by the adjustment screw;

a compression spring between the annular flange of the spring retainer and the other of the pair of cylindrical guides urging the spacing projection on the one guide against the closed end wall of the tubular cylinder;

a housing having a cavity therein forming side portions, end portions and a bottom portion;

a pair of spaced supporting walls extending transversely across the bottom portion upward in the cavity of the housing and forming a recess therebetween;

said walls having notches receiving and guiding the tubular enclosure of the contact unit;

a resilient potting compound in the recess securing and supporting the sealed contact unit;

said bottom portion having a pair of bores with beveled entrances receiving the bent end portions of the rigid leads;

one of said pair of bores having a diameter with a close tolerance to a respective bent end portion of the rigid leads for aligning the sealed contact unit in a predetermined rotative position about the enclosure axis;

the other of said pair of bores having a diameter with a larger tolerance to a respective bent end portion;

a pair of flat elongated terminals secured in and extending through the bottom portion perpendicular to the enclosure axis on opposite sides of the supporting walls;

a pair of flexible electrical conductors electrically connecting the respective rigid leads to inside portions of the respective terminals;

said terminals having portions extending outside the bottom portion for connecting to electrical circuitry;

a protective wall surrounding the outside portion of the terminals;

an insulating and vibration energy adsorbing sheet in the cavity disposed over the sealed switch unit;

a pair of upward and inward extending projections from the bottom portion and the respective end portions supporting the ends of the tubular cylinder;

a pair of guide projections extending inward the cavity from the side portions retaining the tubular cylinder centrally in the cavity;

a cover for the housing having end tabs;

said end portions of the housing having respective grooves receiving the end tabs;

said cover having wing portions with inward extending lips;

said housing having outward extending flanges in the upper edge of the side portions engaging the inward extending lips of the wing portions to retain the cover on the housing;

a bow spring between the cover and the tubular cylinder urging the tubular cylinder against the insulating sheet;

at least one of said cover and said side portions of the housing having notches receiving the input and exhaust tubes; and

a rigid potting compound in the cavity securing the tubular cylinder. 

1. A pressure responsive magnetic switch comprising a non-magnetic housing having a plurality of wall portions forming a cavity; a magnetically operated switch contact unit; a plurality of first projections extending into the cavity from the wall portions and supporting the switch contact unit in a first location in the cavity; a switch operator including a tubular non-magnetic cylinder, a permanent-magnetic piston slidable in the cylinder, and first and second conduits communicating with respective ends of the tubular cylinder; a plurality of second projections extending into the cavity and retaining the tubular cylinder in a second location in the cavity adjacent the switch contact unit; terminal means mounted in the housing and extending outside the housing from the cavity; and means in the cavity electrically connecting the switch contact unit to the terminal means.
 2. A pressure responsive magnetic switch as claimed in claim 1 wherein the magnetically operated switch contact unit includes a tubular non-magnetic sealed enclosure, a pair of magnetic reed contacts, and a pair of leads attached to the respective reed contacts and extending through seals of the enclosure; and each of the plurality of first projections has a groove for retaining the sealed enclosure.
 3. A pressure responsive magnetic switch as claimed in claim 2 wherein the non-magnetic housing is elongated and has a pair of opposite side wall portions, a pair of opposite end wall portions and a bottom wall portion forming the cavity, the plurality of first projections includes a pair of parallel ribs transverse to the side wall portions and extending upward from the bottom wall portion, said groove is formed in the top of the parallel ribs, and the plurality of second projections includes a pair of projections adjacent the respective opposite end wall portions extendiNg upward from the bottom wall portion to a height above the parallel ribs.
 4. A pressure responsive magnetic switch comprising a pair of magnetic switch contacts, a non-magnetic tubular cylinder having an integrally formed wall closing one end, means mounting the pair of magnetic switch contacts adjacent the tubular cylinder, a plug secured in and sealing the other end of the tubular cylinder, a first tube communicating into the tubular cylinder adjacent the one end, a second tube communicating into the tubular cylinder adjacent the other end, and a piston including a permanent magnet slidably supported in the tubular cylinder.
 5. A pressure responsive magnetic switch as claimed in claim 4 wherein the tubular cylinder has an enlarged tubular portion at the other end forming a shoulder at the edge of the enlarged tubular portion, and an inwardly deformed lip securing the plug in the other end against the shoulder.
 6. A pressure responsive magnetic switch comprising a pair of magnetic switch contacts, a non-magnetic tubular cylinder having an integrally formed wall closing one end, means mounting the pair of magnetic switch contacts adjacent the tubular cylinder, a plug secured in the other end of the tubular cylinder, said plug having a threaded bore coaxial with an axis of the tubular cylinder, a first tube communicating into the tubular cylinder adjacent the one end, a second tube communicating into the tubular cylinder adjacent the other end, a piston including a permanent magnet slidably supported in the tubular cylinder, an adjustment screw in the threaded bore having an end extending into the tubular cylinder, a spring retainer movably engaged by the end of the adjustment screw in the tubular cylinder, and a compression spring between the spring retainer and the piston.
 7. A pressure responsive magnetic switch comprising a magnetically operated switch contact unit, a non-magnetic tubular cylinder, means mounting the switch contact unit along side of the tubular cylinder, a first conduit communicating into one end of the tubular cylinder, a second conduit communicating into the other end of the tubular cylinder, a cylindrical permanent magnet in the tubular cylinder, a pair of guides having a pair of facing cylindrical cavities receiving respective ends of the cylindrical permanent magnet and slidably supporting the cylindrical magnet in the tubular cylinder, a resilient cup washer, a rigid backup washer, and means securing the backup washer and the cup washer to one of the pair of guides to form a piston seal in the tubular cylinder.
 8. A pressure responsive magnetic switch as claimed in claim 7 wherein the securing means includes a cylindrical extension on one of the guides extending coaxial with the tubular cylinder and upon which the cup washer and backup washer are mounted, a staked end portion of the cylindrical extension securing the backup washer and the cup washer to the one guide.
 9. A pressure responsive magnet switch comprising a sealed contact unit including a sealed tubular enclosure of glass, a pair of resilient magnetic reed contacts extending into an overlapping relationship within the enclosure, and a pair of leads attached to the reed contacts extending through seals at the respective ends of the enclosure; a housing made from a rigid non-magnetic material; means including a resilient material mounting the contact unit on the housing; a switch operator including a rigid non-magnetic tubular cylinder, a piston having a permanent magnet slidable in the tubular cylinder, and tubular means communicating with respective ends of the tubular cylinder; means mounting the switch operator on the housing such that the resilient material urges the sealed tubular enclosure toward the switch operator; a vibration energy absorbing non-magnetic material between the coNtact unit and the switch operator; and said means mounting the switch operator holding the switch operator against one side of the vibration energy adsorbing material.
 10. A pressure responsive magnetic switch as claimed in claim 9 wherein the energy absorbing material is a sheet of vulcanized fiber.
 11. A pressure responsive magnetic switch as claimed in claim 9 wherein the resilient material is a resilient potting compound, and the means mounting the switch operator includes a rigid potting compound.
 12. A fluid pressure responsive switch device comprising an elongated sealed magnetic contact unit having a non-magnetic tubular glass enclosure with a pair of resilient magnetic reed contacts extending in opposite directions from overlapped contact portions substantially parallel to an axis of the tubular enclosure; a pair of rigid leads attached to the respective pair of resilient reed contacts and extending in opposite directions along the enclosure axis through respective seals at the ends of the tubular enclosure; said pair of leads having end portions bent perpendicular to the enclosure axis to extend in the same direction from the enclosure axis; a non-magnetic tubular cylinder having a cylinder axis and an integrally formed closed end wall and having an enlarged cylinder portion adjacent to the other end forming an annular shoulder; an inlet tube communicating radially into the tubular cylinder adjacent the closed end wall; an exhaust tube communicating radially into the enlarged cylinder portion of the tubular cylinder; a cylindrical permanent magnet; a pair of non-magnetic guides having cylindrical cavities coaxial with the cylinder axis; said guides having bosses projecting radially inward the cavities frictionally retaining respective ends of the cylindrical permanent magnet; a cylindrical extension on one of said pair of guides coaxial with the cylinder axis; a resilient cup washer on the cylindrical extension; a backup washer on the cylindrical extension; a staked shoulder portion of the cylindrical extension securing the backup washer and resilient cup washer to the one guide; a spacing projection extending from the one guide coaxially with the cylinder axis; said pair of guides, permanent magnet, cup washer, and backup washer forming a magnetic slidable piston in the tubular cylinder; a plug in the enlarged cylindrical portion; an annular lip on the end of the enlarged cylindrical portion securing the plug between the annular lip and the annular shoulder; said plug having a channel formed in the periphery thereof allowing communication from the interior of the tubular cylinder to the exhaust tube; a threaded bore extending through the plug coaxial with the cylinder axis; an adjustment screw extending from the threaded bore into the interior of the tubular cylinder; a spring retainer in the tubular cylinder and having an annular flange and a cup shaped center engaged by the adjustment screw; a compression spring between the annular flange of the spring retainer and the other of the pair of cylindrical guides urging the spacing projection on the one guide against the closed end wall of the tubular cylinder; a housing having a cavity therein forming side portions, end portions and a bottom portion; a pair of spaced supporting walls extending transversely across the bottom portion upward in the cavity of the housing and forming a recess therebetween; said walls having notches receiving and guiding the tubular enclosure of the contact unit; a resilient potting compound in the recess securing and supporting the sealed contact unit; said bottom portion having a pair of bores with beveled entrances receiving the bent end portions of the rigid leads; one of said pair of bores having a diameter with a close tolerance to a respective bent end portion of the rigid leads for aligning the sealed contaCt unit in a predetermined rotative position about the enclosure axis; the other of said pair of bores having a diameter with a larger tolerance to a respective bent end portion; a pair of flat elongated terminals secured in and extending through the bottom portion perpendicular to the enclosure axis on opposite sides of the supporting walls; a pair of flexible electrical conductors electrically connecting the respective rigid leads to inside portions of the respective terminals; said terminals having portions extending outside the bottom portion for connecting to electrical circuitry; a protective wall surrounding the outside portion of the terminals; an insulating and vibration energy adsorbing sheet in the cavity disposed over the sealed switch unit; a pair of upward and inward extending projections from the bottom portion and the respective end portions supporting the ends of the tubular cylinder; a pair of guide projections extending inward the cavity from the side portions retaining the tubular cylinder centrally in the cavity; a cover for the housing having end tabs; said end portions of the housing having respective grooves receiving the end tabs; said cover having wing portions with inward extending lips; said housing having outward extending flanges in the upper edge of the side portions engaging the inward extending lips of the wing portions to retain the cover on the housing; a bow spring between the cover and the tubular cylinder urging the tubular cylinder against the insulating sheet; at least one of said cover and said side portions of the housing having notches receiving the input and exhaust tubes; and a rigid potting compound in the cavity securing the tubular cylinder. 